Create Your Own create-react-app CLI

Most technologies have a CLI to create a new workspace. In fact, it is so prevalent that NPM and other package managers support it natively. For example:

• Nx has create-nx-workspace
• React has, well, had create-react-app
• Angular has Angular CLI
• Vite has create-vite

Having a CLI to quickly scaffold a starting project is great for onboarding new people, but it can also be a burden for framework authors as they want to rather focus on building the framework. Additionally, building and supporting a good CLI is another beast to tackle. And this is where Nx comes in.

Nx has had support for creating custom “presets” for a while, allowing plugin authors to fully customize the workspace structure from the ground up. To use them you had to go via the create-nx-workspace command though, passing the name of your plugin as the --preset . This works, but you might want to have a more “branded command” experience, like npx create-my-own-app .

And this is exactly what we’re going to explore in this article. We will write our own CLI. And out of nostalgia, let’s build our own version of Create-React-App.

If you want to check out the final result, here’s the corresponding Github repo: https://github.com/nrwl/nx-recipes/tree/main/nx-devkit-create-own-cli

Prefer a video? We got you covered!

What is Nx and what is an Nx plugin?

But before we jump right into the topic, what is Nx? And more specifically, what are Nx Plugins?

Nx is an open-source build system that provides tools and techniques to enhance developer productivity. Check out this 10 min video overview of Nx if you want to learn more.

Our example, in particular, uses Nx as a dev tool for creating a CLI and plugin. Nx plugins are npm packages that provide integrations between Nx and other technologies. You can use Nx without them, but they can provide great value if applied properly. my-own-react is the plugin to integrate React and Nx.

Step 1: Create a CLI workspace

Create a new Nx workspace that is preconfigured for plugin development, using the below command:

Note, if you already have an existing Nx plugin workspace, instead of creating a new workspace, you can simply run the following in your plugin repository to generate the create CLI:

Project graph of the workspace

The resulting workspace contains 2 projects: a CLI and an Nx plugin.

• create-my-own-react-app: The CLI project. It contains the code to run when developers invoke npx create-my-own-react-app. This will set up a workspace for the developer.
• my-own-react: Nx plugin to integrate react with Nx. It will contain the code for creating and serving an app. It is under the src folder. This will be installed in the user’s workspace.

CLI Package Structure

Let’s focus on the create-my-own-react-app project which is our CLI.

The index.ts file is the key part here. It is the one that gets invoked when someone runs npx create-my-own-react-app later once we publish it.

The main chunk of code is createWorkspace(`my-own-react@${presetVersion}`). This function creates an Nx workspace with the my-own-react plugin installed.

1. createWorkspace will also generate the preset generator defined by my-own-react located at src/generators/preset/generator.ts. This is the logic which scaffolds a project which uses your technology.

Step 2: Run the CLI Locally

To properly test your CLI you can either publish it to NPM as a beta version or use a local npm registry like Verdaccio. Luckily our Nx workspace already comes with a feature to make that a seamless process.

1. First, start a local Verdaccio-based npm registry using the following command:

This will start the local registry on port 4873 and configure npm to use it instead of the real npm registry.

2. In the second terminal, run the command to publish all the projects:

(Note, _publish_ is a target defined in the _project.json_ of our projects.)

This command will publish both my-own-react and create-my-own-react-app packages to your local registry. If open the running Verdaccio registry at http://localhost:4873 you should see the published packages.

3. Now, you can run npx create-my-own-react-app just like a developer using our CLI would. For example, go to the tmp directory and create a my-own-react workspace named test:

What you’ll get is an Nx workspace with the base setup and a test library project with a single TS file. Because that’s exactly what our current preset generator does.

Let’s fix that in the next step.

Step 3: Change the CLI to Setup a React App

In this step, we dive a bit more into the actual Nx plugin development to create our CRA replica.

We’ll go rather quickly but if you want a slower walkthrough you might be interested in this video that leverages a generator for automating the creation of projects. Exactly what we’re going to do in our preset now.

To do this, we will fill in the preset generator under src/generators/preset

A generator is a function that makes modifications to a file system representation known as the Tree. These modifications will then be applied to the real file system. In our case, the preset generator will create the files for a React app.

Currently, the file at src/generators/preset/generator.ts looks like:

The preset generator does 2 things:

• Create an Nx project using the addProjectConfiguration function. This creates a project.json file which allows Nx to run commands on it.
• Generates files in the project using the generateFiles function. This uses the templates under src/generators/preset/files which are interpolated to become the files that are generated for the user.
• Format the generated files with prettier with the formatFiles function

preset generator

The addProjectConfiguration and generateFiles functions are from @nx/devkit, a library that contains utility functions for writing plugins for Nx. For the future, see the complete list of utility functions.

1. Change the project which is created with addProjectConfiguration:

• The projectRoot will be ‘.’, the root of a workspace
• The projectType changes to application

2. Next, change the files generated into the project under src/generators/preset/files. We will use the same template as create-react-app .

Rename the existing index.ts.template to src/generators/preset/files/src/index.tsx.template and add the following content:

Add another file to generate a CSS template at src/generators/preset/files/src/index.css.template:

And finally, another file to host the actual HTML template: src/generators/preset/files/public/index.html.template:

3. Our application uses some npm dependencies so add those to the workspace as well with the addDependenciesToPackageJson function to the end of the export default function in src/generators/preset/generator.ts:

This line will add the latest react, react-dom, react-scripts, and their types to the package.json in the generated workspace.

Final Preset Generator

Now src/generators/preset/generator.ts should look like this:

Step 4: Run the New Version that Creates the React App

Now you can publish a new version of my-own-react and create-my-own-react-app and run it again:

The CLI now creates a workspace with the dependencies we want and the code for the react application just like create-react-app:

Step 5: Add a Serve Target

The workspace setup is done, what we’re missing though is a way to easily serve our app. To stick to what CRA does we simply need to run react-scripts start , but ideally, we want to make that more convenient for the developer by pre-generating that script into the workspace.

We have two possibilities:

• add the script to the root-levelpackage.json using the updateJson function exposed by @nx/devkit
• add a target to the project.json using the addProjectConfiguration function exposed by @nx/devkit

Nx can use both. The project.json is Nx’s variant of a more evolved package.json scripts declaration, that allows to specify metadata in a structured way.

To keep things simple, let’s just generate a new script for the root-level package.json. We need to modify our src/generators/preset/generator.ts as follows:

Note, we want to keep our project.json file even though it doesn’t have any targets defined. That way Nx recognizes it as a proper project and applies caching and other optimization strategies.

Adding the target to the project.json rather than package.json

Alternatively, we could have adjusted the already present addProjectConfiguration function to add the react-scripts command:

Step 6: Run it Again to Get a React App That Can Be Served

To test our changes, let’s publish a new version and run it again.

Once we generate a new workspace with the new preset version (npx create-my-own-react-app@1.0.2 test3), we should now see our package.json startscript being generated.

To run the app we either run

• npm start
• or npx nx start which would automatically pick up the start script in the package.json

serve output

Step 7: Add a Prompt to the CLI to Customize the Starter App

Now, you have a CLI that creates a workspace that users can use to get started with React. But that’s not all. Let’s take it a step further and make it interactive by adding a prompt that can let different users customize the kind of workspace that they want to create.

Take a look at the CLI code at create-my-own-react-package/bin/index.ts, you will notice it is pretty barebone. It reads thename from the command’s arguments.

You can use libraries like enquirer (or even fancier ones like Clack) to prompt developers for options. For this example, prompt developers to select a light or dark theme for the starter app.

1. Install enquirer with npm i enquirer
2. Change create-my-own-react-package/bin/index.ts to import enquirer and prompt developers to enter the mode option:

You can assemble options for createWorkspace; however, you’d like and they will be passed to the my-own-react preset.

3. Change src/generators/preset to accept this option and apply it.

In src/generators/preset/schema.d.ts, add it to the type for the options:

Also, change the CSS for .App-header in the CSS template filesrc/generators/preset/files/src/index.css.template:

Now if you republish the projects and regenerate an app with the light mode, you should see the background color and text color of the header got changed:

serve output

Step 8: E2E Testing

This is how users start using your technology so you should write e2e tests to ensure this does not break. This workspace was also generated with a testing file packages/my-own-react-e2e/tests/create-my-own-react-app.spec.ts.

You can modify this e2e test to test your CLI. Then, run it using the command npx nx e2e my-own-react-e2e. Before the tests run, as a global setup, a local registry is started and the packages are published.

The default test works like this:

1. Creates a test workspace at tmp/ using the create-my-own-react-app CLI
2. Runs npm ls my-own-react to validate that the plugin is installed in the test workspace
3. Cleans up the test workspace

Make sure dark is passed into create-my-own-react-app :

Add to a test to check react and react-dom are installed:

Recap and next steps

Recap:

• We learned about what an Nx Plugin is and generated a new plugin workspace
• We generated a new CLI package into the workspace: create-my-own-react-app . This allows our users to easily scaffold a new workspace
• We adjusted the preset generator to setup a CRA-like React setup
• We wrote some e2e tests to ensure that things do not break

This should give you a good insight into how to get started. But there’s more to explore:

• We could provide more [generators](/plugins/recipes/local-generators) to our users that help with setting up new components, adding unit tests, configuring the React Router etc.
• Add a generator to add other Nx plugins such as Jest, ESLint, or Cypress
• We could also include “executors”, which are wrappers around tasks to abstract the lower-level details of it
• etc.

Now clearly this was a simple example of how you could build your own CRA using Nx. If you want to see a real-world React setup powered by Nx, check out our React Tutorial: /getting-started/tutorials/react-standalone-tutorial

Learn more

• 🧠 Nx Docs
• 👩‍💻 Nx GitHub
• 💬 Nx Official Discord Server
• 📹 Nx Youtube Channel
• 🚀 Speed up your CI